1. Field of the Invention
The present invention is directed to a two-stage reciprocating compressor and the application of such compressors to heating and air conditioning systems and methods. One aspect of the invention is concerned with stabilizing such compressors when the stroke length of one or more reciprocating pistons is switched to change the compressor capacity. Another aspect is the improved throw blocks and lubrication systems for such compressors. Another aspect of the invention concerns a unique electrical circuitry for operating the crankshaft drive motor of the compressor, whereby reversal of the motor for reducing or eliminating the throw takes the motor off the normal run winding and places it on a more efficient winding of reduced current capacity, in particular, the start winding.
Another aspect of the invention is the application of two-stage compressors of the present invention to novel air conditioning and/or heat pump systems and methods. Preferably, such systems include additional two-stage components.
2. Background
The present invention is directed to two stage reciprocating compressors, including scotch yoke compressors such as shown in U.S. Pat. No. 4,838,769. In such machines the reciprocating motion of the pistons is effected by the orbiting of crankpins which are attached to said pistons by connecting rods or other connecting structures having bearings rotatably mounted on said crankpins.
The compressors of the present invention include gas compressors, especially multi-cylinder refrigerant compressors, in which the connecting rod bearing of at least one piston is mounted on an eccentric cam rotatably mounted on the crankpin. This cam angularly adjusts upon reversal of the crankshaft drive motor and the crankshaft to switch to either a lengthened or shortened crankpin throw and piston stroke. Such stroke or throw switching can be engineered to give desired high pressure refrigerant output capacities such that the compressor efficiency can be maintained more easily under varying load requirements.
Throw switching compressors for which the present invention finds particular application are shown and described in U.S. Pat. Nos. 4,479,419; 4,236,874; 4,494,447; 4,245,966; and 4,248,053, the disclosures of which are hereby incorporated herein by reference in their entirety. With respect to these patents the crankpin journal is complex and comprised of an inner and one or more outer eccentrically configured journals, said inner journal being the outer face of the crankpin shaft, and the outer journal(s) being termed xe2x80x9ceccentric cams or ringsxe2x80x9d in these patents, and being rotatably mounted or stacked on said inner journal. The bearing of the connecting rod is rotatably mounted on the outer face of the outermost journal.
In these patents, as in the present invention, all journal and bearing surfaces of the power transmission train of the shiftable throw piston from the crankshaft to the connecting rod are conventionally circular and allow structurally unhindered rotative motion, within design limits, of the outer journal(s) on the inner journal and of the connecting rod bearing on the outermost journal. This rotative motion, in either direction, will, thru the eccentricity of the outer journal surface of the outermost journal relative to its inner bearing surface, shift the radial distance of the orbital axis of the crankpin from the axis of rotation of the crankshaft and thus change the throw of the crankpin and the stroke of the piston.
As described in, e.g., U.S. Pat. No. 4,479,419 and with reference to the structure numbering therein, the angular positioning of the cam 38 on the crankpin 34 is accomplished by providing a pair of drive stops (not numbered in the said U.S. Pat. No. 4,479,419 patent, but numbered 58, 60 in the U.S. Pat. No. 4,494,447 patent as xe2x80x9cend pointsxe2x80x9d) which are angularly spaced on a portion of the crankshaft such as the crankpin 34, and a driven dog 48 provided on the cam 38. These stops an d the dog are angularly positioned with respect to each other such that upon rotation of the crankshaft in one direction one of the stops will first engage one side of the dog and rotate cam 38 to a first prescribed angular position on the crankpin to produce one piston stroke length. Conversely, reversing the rotation of the crankshaft will terminate this first engagement and cause the other of the stops to rotate to and engage an opposite side of the dog and rotate the cam to a second prescribed angular position on the crankpin to produce another piston stoke length. These angular positions are alternatively characterized herein as xe2x80x9cend point(s)xe2x80x9d or xe2x80x9cdog-stopxe2x80x9d junction(s) or xe2x80x9ccontact junction(s)xe2x80x9d, all hereinafter termed xe2x80x9cjunction(s)xe2x80x9d.
It is noted that at least a portion of the rotation of the cam relative to the crankpin to either of its endpoints can also result from the inertia of the cam or the rotational drag of the strap end bearing of the connecting rod acting on the outer journal surface of the cam.
It is apparent that for a given fixed crankpin throw the maximum possible magnitude of the piston stroke shift will depend on the degree of eccentricity between inner bearing surface and the outer journal surface of the cam. A larger eccentricity will allow an increased or reduced throw depending on the angular position of the cam on the crankpin. Therefore, a properly configured eccentricity will allow the said orbital axis of the crankpin to become coincident with the axis of the crankshaft, thus bringing the crankpin throw and the piston stroke to zero, and thus pacifying the throw, piston and cylinder. It is noted that in this zero stroke or passive mode, the completely pacified piston will remain, theoretically, one half way between its normal top dead center and normal bottom dead center positions during further operation of the compressor in the reduced capacity mode.
It is to be particularly noted, that as mentioned above, all of the journals and bearings involved in this power transmission train are essentially perfectly circular within, of course, modem machining capability, and their rotational contacts with one another are practically frictionless. Thus arises the conundrum that if only one side of the dog is in engagement with a stop at any given time, what is to prevent disengagement of the junction and the consequent rotation of the cam on the crankpin during periods when the cam is being driven by the stop with only minimal force? Such a disengagement could produce a plethora of unplanned piston movements or strokes, which could significantly thwart the effort to maintain maximum compressor efficiency under varying load requirements. Based on a review of the above patents, it apparently was believed that the junction can be maintained simply by the inertia of the cam during such periods.
The U.S. Pat. No. 4,494,447 patent alludes to a destabilizing phenomena, and then only with a glancing mention in column one that gas thrust, piston rod inertia, and centrifugal and gas torque reversal forces contribute to cam instability. In what context and in what relationship however to, e.g., a zero stroke piston mode is not readily apparent from this patent. Also, in column one of that patent it is stated that xe2x80x9cxe2x80x94forces which generally tend to prevent the possibility of oscillation are friction forces, various drag loads, and cam inertia forces.xe2x80x9d This statement appears to be a recitation of those forces which are inherently present, in varying degrees, in all refrigeration compressors, and shed no light on a solution to the instability problem, particularly with respect to a zero piston stroke mode.
This patent then goes on the disclose an actual stabilizing structure constituting its invention, which structure is characterized as aiding in holding the cam in the desired position. This structure comprises end stops 58, 60 which are preferably spaced about 270xc2x0 apart such that according to the patent a substantial centrifugal force torque xe2x80x9cCFTxe2x80x9d will develop tending to maintain the stops and dog in contact at the endpoints of the cam rotation, as shown in FIGS. 4 and 5 of the patent. Also as disclosed in this patent, this CFT can be generated by repositioning the center of mass 62 of the cam away from the throw axis which passes thru the crankshaft axis 30a and the crankpin axis 32a, as shown in FIGS. 6 and 7 of the patent.
Applicants have found that with such complex crankpin journals under typical compressor operating conditions, cam inertia alone is ineffective to prevent disengagement, i.e., instability of the junction and the throw shift under the dynamic forces present, even in a theoretically completely pacified cylinder. These compressors have also not been perfected to the extent that they have been used successfully in the marketplace.
In short, while the general concept of two stage compressors is disclosed in the prior art, there exists considerable needs for improvement in these compressors, as to their structure, characteristics, and application in HVAC systems and methods.
One object of the invention is to provide a crankpin throw shifting structure for at least one crankpin of a multicylinder compressor. The structure overcomes the negative effects of destabilizing forces developed during either the passive or active mode of the piston operation and minimizes or eliminates noise which otherwise would be generated by repeated remakings of the stopxe2x80x94dog junction during operations in either of said modes. Another object is to provide a stabilizing structure whereby in the passive mode the piston has essentially a zero piston stroke. Yet another object is to provide such a stabilizing structure that can be applied with little alteration of the other components of reversible, two stage compressors.
An additional object is to provide improved lubrication systems for the crankpin and eccentric cam assembly of two stage compressors. Another object is to provide an improved assembly of eccentric cams and crankpins for two-stage reciprocating compressors and methods for assembling such compressors.
Still another object is to provide an efficient drive motor reversing system for compressor alternating between full capacity and reduced capacity. Another object is to provide a protector system for the motor control. Yet another object is to provide a motor control that can economically and efficiently operate a number of different two-stage HVAC components, such as compressors, evaporator blowers, condenser fans, and the like.
Further objects of the invention are to apply the two-stage compressor of the present invention to improved air conditioning and/or heat pump systems and methods. Related objects are to provide efficient and economical HVAC systems with two-stage characteristics for a wide variety of refrigerants, including systems that increase the efficient use of R-410.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a two stage reciprocating compressor comprising a block having at least one cylinder and an associated compression chamber and piston, a crankshaft including an eccentric crankpin, a reversible motor for rotating that crankshaft in a forward and a reverse direction, and an eccentric, two position cam rotatably mounted over the crankpin. The cam rotates to and operates at a first position relative to said crankpin when the motor is running in the forward direction and rotates to and operates at a second position relative to said crankpin when the motor is running in the reverse direction. The eccentricities of said crankpin and said cam combine to cause the piston to have a first stroke when the motor operates in the forward direction and a second stroke when the motor operates in the reverse direction. The second stroke is less than the first stroke, and in some embodiments is zero. The compressor also includes a control for selectively operating the motor either in the forward direction at a first, preselected, fixed power load or in the reverse direction at a second, preselected, fixed power load. The second power load is less than the respective first power load.
In a preferred embodiment, the motor that runs the compressor is an induction motor having start and run windings. The motor operates in the forward direction on the run winding and in the reverse direction on the start winding. These run and start windings are preferably selected to keep the motor at optimum possible efficiency when operating at both stages. The motor control includes a switching control to switch the operation of the motor from run to start windings, based on known or sensed conditions. This control circuit arrangement provides a single and effective way to provide two-stage operation of a compressor, as well as other HVAC components such as blowers and fans.
The motor and its two stage control are preferably applied to a two stage reciprocating compressor with a two-position eccentric cam that serves to adjust the stroke of at least one piston in the compressor. The compressor preferably includes stabilization means that include a first stop mechanism for restricting the relative rotation of the cam about the crankpin, when the motor is running in the forward direction, and a second stop mechanism for restricting the relative rotation of the cam about the crankpin, when the motor is running in the reverse direction. In one embodiment, the first stop mechanism is in the form of an eccentric mass formed on the eccentric cam, and the second stop mechanism is in the form of a pressure relief system for relieving any significant pressure differential between the low side of the compressor and the compression chamber of the pacified piston.
In addition, the invention comprises a protection for the motor. The protected motor comprises a single phase reversible induction motor having start and run windings and designed to operate on the run windings when rotating in one direction and on the start windings when rotating in the second direction. The motor circuiting includes a protector having an enclosure holding a heat sensitive switch and a pair of heaters. The heaters, preferably in the form of resistors, are connected to the heat sensitive switch at one end and respectively to the start and run windings of the motor at the other end. When the internal temperature of the protector reaches a preselected temperature, the heat sensitive switch operates to open the circuit and remove the windings from power for a preselected period of time. Preferably, the motor is applied to run a two stage reversible motor, and the protector and motor are encased in the compressor housing.
Another aspect of the invention is a crankshaft and cam assembly for a variable load compressor having at least one cylinder and an associated piston driven by the combination of a crankpin and an eccentric cam on the crankpin. The crankshaft comprises a shaft with a proximal end and a distal end with at least one eccentric crankpin formed between the proximal and distal ends. Stops are formed on or adjacent the crankpin at a pair of angularly separate points. The eccentric cam rides on the crankpin and has a diameter equal to or larger than the diameter of the crankshaft at its distal end. The cam includes a pair of dogs for selective engagement with the stops on the crankpin. The system includes a mechanical system for holding the cam in its axial position on the crankpin, when the two are assembled.
In one embodiment the mechanical system includes an end cap fixed to the shaft. In other embodiments, the mechanical system includes a radial hole formed in the crankpin and a pin that extends into the radial hole of the crankpin and slides within the internal slot. Additional embodiments are described below.
Another aspect of the invention is a lubrication system for applying lubricant to the engaging surfaces of the crankshaft and cam and between the cam and the bearing surface of the connecting rod of the two stage compressor of the present invention. In one embodiment the lubricating system includes an elongated axial supply formed in the crankshaft, a cross drill formed in the crankshaft and in fluid communication with the axial supply and an outer surface of the crankpin, and an oil communication hole formed in the cam. The oil communication hole is aligned with the radial cross drill in the crankshaft, when the cam is in both the first and second positions, and is in fluid communication with the bearing surface of the connecting rod in both positions. Other embodiments of the lubricating system are contemplated and described below.
The invention further comprises the application of a two stage compressor, particularly the two stage compressor of the present invention to air conditioning systems and methods. The invention thus includes a system for cooling a space comprising a two stage compressor that operates either at a first fixed maximum load or at a reduced second load, an expansion device, an evaporator, and a condenser, in a refrigeration loop with the compressor. The system also includes a two stage evaporator blower that operates either at a first fixed maximum load or at a second reduced fixed power load. The air conditioning system also includes a control system interconnected with the compressor and blower and designed to operate the compressor and blower at the respective first stages when the cooling requirement exceed a preselected value and at the respective second stages when the cooling requirements fall below that preselected value.
Preferably, the first and second stages of the compressor and the blower are matched to provide optimum efficiency for the cooling requirements of the system. The compressor of the system preferably is a reversible two stage reciprocating compressor of the present invention. The control preferably is provided by a two stage thermostat, and the expansion valve preferably is a two stage device. The cooling system of the present invention can be used with the wide variety of refrigerants and applies R-410 refrigerant more efficiently than conventional systems.
In addition, the invention includes the application of two stage compressors to heat pump systems and methods. The invention thus includes a heat pump system comprising a two-stage compressor, condenser, an expansion device, an evaporator, and means for operating the compressor, condenser, expansion device, and an evaporator as a heat pump that can selectively provide air conditioning and heating, as required. The system includes a control system for operating the system in a heating mode with the compressor running at the first stage or the second stage, based upon the heating requirements, and for operating the system in an air conditioning mode with the compressor running only at the first stage. The heat pump system preferably has a single orifice expansion valve, and the compressor preferably operates at 60% to 70% capacity in the air conditioning mode. Preferably, the two stage reversible compressor of the present invention is applied to this system.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one (several) embodiment(s) of the invention and together with the description, serve to explain the principles of the invention.